1. Field of the Invention
This invention relates to a connection structure of an electrical component such as a variable resistor.
2. Description of the Related Art
A connection structure of a conventional electrical component is described herein under with reference to FIG. 6 to FIG. 10 in which a variable resistor is exemplified.
A base plate 21 formed of a molded synthetic resin is flat and has a hole 21a at the center, and a U-shaped resistor (not shown in the drawing) and a circular collector (not shown in the drawing) are provided on the upper side of the base plate 21.
Terminals 22 and 23 are embedded on the base plate 21, the terminal 22 is connected to the collector and the terminals 23 are connected to the resistor.
A cover 24 formed of molded synthetic resin has a flat wall 24a, a side wall 24b which extends from the periphery of the flat wall 24a downward, a plurality of snaps 24c which extend downward from the bottom end of the side wall 24b, and a hole 24d formed at the center of the flat wall 24.
The cover 24 covers the top side of the base plate 21 so as to cover the resistor and collector, and is fixed to the base plate 21 by snapping the snaps on the periphery of the base plate 21.
The first connection member 25 consisting of polyacetal synthetic resin which constitutes a rotor has a sleeve 25b having a non-circular hole 25a and a plate 25c which extends radially from the sleeve 25b, and a moving contact 26 having contacts 26a and 26b is embedded on the connection member 25.
The connection member 25 is inserted supportingly to the hole 21a of the base plate 21 and the hole 24d of the cover 24, and attached rotatably to the base plate 21 and the cover 24.
When the connection member 25 is attached, the contact 26a is brought into contact with the collector slidably and the contact 26b is brought into contact with the resistor slidably.
The second connection member 27 which constitutes a shaft consists of metal material or synthetic resin material, and has a non-circular end 27a.
Because the first connection member 25 is formed of polyacetal synthetic resin, if the clearance between the hole 25a of the first connection member 25 and the end 27a of the second connection member 27 is zero, the end 27a is not inserted into the hole 25a, therefore a clearance K is provided between both members, and the end 27a is inserted into the hole 25a to connect the first connection member 25 to the second connection member 27.
When the second member 27, which is a shaft, is rotated, the first connection member 25, which is a rotor, is rotated, and the contacts 26a and 26b of the moving contact 26 are slid on the collector and resistor respectively with the rotation to change the resistance value.
Next, a method for fabrication of the first connection member 25 is described with reference to FIG. 10. A metal mold 28 comprises an inner mold 28a provided at the center for forming the hole 25a of the first connection member 25, and an outer mold 28d having a cavity 28b for forming the sleeve 25b and plate 25c and a gate 28c for injecting hot molten resin into the cavity 28b. Next, when molten polyacetal synthetic resin is injected into the cavity 28b from the gate 28c, polyacetal hot molten resin is jetted against the inner mold 28a and the stream is branched toward the arrow directions, the branched streams merge and are mixed at the position G located on the opposite side with the gate 28c, and then polyacetal synthetic resin is solidified and thus the molding of the first connection member 25 is completed.
Because polymer molecules of the polyacetal synthetic resin are entangled each other in molten state and solid state, when streams are merged at the position G on the opposite side with the gate 28c, the streams are mixed completely and form a molded product having no weld mark. Therefore, the sleeve 25b of the first connection member 25 exhibits little deformation, as the result, press fitting of the second connection member 27 into the sleeve 25b of the first connection member 25 having the structure as described above is difficult, and the first connection member 25 engages the second connection member with a play gap.
Because the first connection member 25 is formed of acetal synthetic resin, press fitting of the second connection member 27 into the first connection member 25 is difficult in the conventional connection structure of an electrical component, both members are connected with play and engaged with play.
The rotation of the second connection member 27 is transmitted to the first connection member 25 with play, and the rotation transmission is not correct.